The present invention generally relates to the area of diagnostic medical equipment, and more particularly to diagnostic devices for identifying problematic blockages within coronary arteries by means of a sensor mounted upon the end of a flexible elongate member such as a guide wire.
In the past decade, innovations in the diagnosis of cardiovascular disease have migrated from external imaging processes to internal, catheterization-based, diagnostic processes. Diagnosis of cardiovascular disease has been performed through angiogram imaging wherein a radiopaque dye is injected into a vasculature and a live x-ray image is taken of the portions of the cardiovascular system of interest. Magnetic resonance imaging (MRI) has also been utilized as well. More recently, however, diagnostic equipment and processes have been developed for diagnosing vasculature blockages and other vasculature disease by means of ultra-miniature sensors placed upon a distal end of a flexible elongate member such as a catheter, or a guide wire used for catheterization procedures.
One such ultra-miniature sensor device is a pressure sensor mounted upon the distal end of a guide wire. An example of such a pressure sensor is provided in Corl et al. U.S. Pat. No. 6,106,476, the teachings of which are expressly incorporated herein by reference in their entirety. Such intravascular pressure sensor measures blood pressure at various points within the vasculature to facilitate locating and determining the severity of stenoses or other disruptors of blood flow within the vessels of the human body. Such devices are commonly used to determine the effectiveness of an angioplasty procedure by placing the pressure sensor proximate a stenosis and measuring a pressure difference indicating a partial blockage of the vessel.
As one can imagine, the aforementioned intravascular pressure sensors are utilized in operating room environments including many types of sensors and equipment for diagnosing and treating cardiovascular disease. Clearly, the room for error is very limited. Therefore, there is substantial interest in simplifying every aspect of the operating room to reduce the incidence of errors.
Notwithstanding the interest to keep equipment simple, there is a necessity to provide an interface device between the intravascular guide wire-mounted pressure sensor and a physiology monitor that displays a human-readable output corresponding to the sensed pressure. The interface device receives synchronization information, in the form of an excitation signal, from the monitor and provides conditioned, standardized output in the form of an analog voltage signal. The interface device drives the guide wire-mounted pressure sensor with a sensor current, conditions a sensed analog sensor input signal, and performs mathematical transformations (by means of a microcontroller) to render the standardized output to the physiology monitor. The interface device thus provides a means for attaching multiple types of sensor devices to a physiology monitor such that input to the physiology monitor is standardized and not dependent upon the sensing device""s signal requirements and operational characteristics.
In a known prior intravascular pressure sensor-to-physiological monitor interface arrangement, marketed by JOMED Inc. of Rancho Cordova, Calif. and depicted in FIG. 1, a signal conditioning interface, comprising an amplifier module 10 (e.g., the Model 7000 Patient Cable) and a WAVEMAP(trademark) processor box 12, is interposed between a physiology monitor 14 and a WAVEWIRE(trademark) pressure sensing guide wire 16. The guide wire 16 is a disposable device connected via a connector 15 to the amplifier module 10. The amplifier module 10 receives power and an excitation signal through two separate and distinct electrically conductive lines within cable 17 connected to distinct output leads of the WAVEMAP(trademark) processor box 12. The WAVEMAP(trademark) processor box receives power from a standard wall outlet 18 via a standard three-pronged (grounded) power cord 20 plugged into the wall outlet 18. Though not shown in the drawing, the physiology monitor is powered via standard AC wall outlet power as well.
The WAVEMAP(trademark) processor box 12 includes a separate and distinct signal interface connected to the physiology monitor 14. The WAVEMAP(trademark) processor box receives a differential voltage excitation signal (either AC or DC) from the physiology monitor 14 via a cable 22. The excitation signal transmitted via the cable 22 is considerably lower power than the AC power deliverable to the WAVEMAP(trademark) processor box 12 from the wall outlet 18 via the power cord 20. The cable 22 also transmits a signal representing sensed pressure (5 microvolts/mmHG) from the WAVEMAP(trademark) processor box 12 to the physiology monitor 14. Yet another cable 24 transmits an aortic pressure (Pa) sensed by another device, from the physiology monitor 14 to the WAVEMAP(trademark) processor box 12. Due to the multiple devices and separate power sources required by the prior known devices, physically setting up the intravascular pressure reading devices can be both complex and cumbersome due to the multiple cords and connections required by this known arrangement. Also, once set up, the multiple cords create clutter within the vicinity of the patient.
A presently used temperature compensation/signal conditioning scheme for a signal conditioning interface (e.g., the above-mentioned WAVEMAP(trademark) processor 12) relies upon a digital processor to compensate for temperature and pressure effects upon a guide wire mounted intravascular pressure sensor. The compensation equation comprises a polynomial including a set of six coefficients for temperature compensation, pressure sensitivity, and temperature effect on pressure sensitivity for each of the two resistive elements in a characterized sensor device. The compensation value is computed for each pressure reading (with constant terms computed in advance to reduce the processing load to the extent possible). Calculating the polynomial result for each pressure reading presents a considerable processing load on a signal conditioning interface processor.
The present invention comprises a signal conditioning device having low power requirements and a simplified connection scheme for interfacing intravascular diagnostic devices, such as a pressure sensor disposed upon a distal end of a guide wire, and a physiology monitor providing an excitation signal for the intravascular diagnostic devices.
The present invention comprises a signal conditioning device that is connected via cables to an intravascular measurement device and a physiology monitor. The signal conditioning device includes a number of analog and digital circuits that cooperate to perform amplification, filtering and/or compensation on signals passed between the pressure sensor and the physiology monitor.
The signal conditioning device includes a sensor interface circuit that supplies a sensor drive signal for energizing a sensor carried by an attachable intravascular measurement device and providing a measurement signal. The conditioning device also includes a physiology monitor interface. The physiology monitor interface includes an input for receiving a sensor excitation signal from the physiology monitor and an output for transmitting an output signal corresponding to sensed measurements provided by the attached sensor arising from the sensor drive signal.
The signal conditioning devices also comprises a power supply circuit interposed between the physiology monitor interface and the signal conditioning circuitry of the signal conditioning device. The power supply circuit includes a signal converter that receives a portion of power supplied by the sensor excitation signal and powers at least portions of the signal processing circuitry within the signal conditioning device with power derived from the portion of power supplied by the sensor excitation signal.
In accordance with another aspect of the new signal conditioning device, a temperature compensating current source within the signal conditioning device provides an adjustment to the current supplied to at least one of a pair of resistive sensor elements of an attached sensor to compensate for differences between temperature change upon the pair of resistive sensor elements, thereby facilitating nullifying temperature effects upon the resistive sensor elements.